1. Field of the Invention
This invention relates to the recovery of iminodiacetic acid and Glauber's Salt (Na.sub.2 SO.sub.4.lOH.sub.2 O) from sodium sulfate solutions such as the liquor generated in the process of producing iminodiacetic acid.
2. Description of the Prior Art
Typical prior art processes for the recovery of iminodiacetic acid from sodium sulfate solutions are disclosed in U.S. Pat. Nos. 3,808,269 and 4,299,978.
U.S. Pat. No. 3,808,269, the disclosure of which is herein incorporated by reference, discloses a process of recovering iminodiacetic acid (IDA) from a starting aqueous solution of sodium sulfate and the amino acid having a temperature above about 33.degree. C. and containing at least 5% amino acid. The process comprises adjusting the pH of the starting solution to 1.5-3 to form an IDA precipitate and a first mother liquor; separating the IDA precipitate from the first mother liquor; and recovering the separated IDA. Sodium sulfate can then be precipitated from the first mother liquor by adjusting the temperature so as to prevent precipitation of IDA.
U.S. Pat. No. 4,299,978, the disclosure of which is herein incorporated by reference, discloses a process for separating an "iminodiacetic acid component" from an aqueous glycine solution including IDA. The process comprises adding sulfuric acid in the presence of a sodium salt to the aqueous solution so as to lower the pH to 1.5 or less, whereby an "iminodiacetic acid component" is crystallized from the solution, and separating the precipitated IDA component. Glycine can thus be efficiently recovered with minimal levels of IDA. Glauber's salt is not generated.
The foregoing references use processes where the precipitation of sodium sulfate with the amino acid is avoided. These processes generate waste liquor streams which include a substantial amount of product. Streams such as this have heretofore been discarded.
Other approaches to the recovery of amino acids include U.S. Pat. No. 3,510,575 where glycine is separated from NH.sub.4 Cl, and U.S. Pat. No. 4,691,054 where amino acids are isolated by ion exchange from systems that are substantially free of inorganic ions (such as sodium sulfate).